This invention relates to a method of evaluating a thin film having optical anisotropy, such as a crystal oriented film for providing crystal particles with an initial orientation.
As a method of evaluating the anisotropic thin film, there is known a method using a reflected light, which is disclosed in such as Japanese Unexamined Patent Publications (JP-A) Nos. 3-65637 (first prior art), 9-218133 (second prior art), 7-151640 (third prior art), and 5-5699 (fourth prior art).
The first prior art discloses a method of measuring anisotropy on the basis of an incident angle and dependency of an incident direction of the reflected light intensity. The second prior art discloses a method of determining dielectric constant, film thickness, and a direction of a main dielectric constant coordinate of an oriented area, and dielectric constant and film thickness of unoriented area. The third prior art discloses a method of measuring the anisotropy in accordance with two color differences by using of a infrared radiation. The fourth prior art discloses a method of measuring the anisotropy by changing the incident angle by using of a visible ray.
As the anisotropic thin film, there is known a crystal oriented film which is subjected to an orientation treatment for use in a liquid crystal display component. A method of evaluating such a film is disclosed in Japanese Unexamined Patent Publication (JP-A) 4-95845 (fifth prior art). Particularly, the fifth prior art discloses a method of evaluating the anisotropy by measuring reflected light intensity which is generated when a linear polarization is projected in the film.
In an inorganic material having high-level crystalline, a relation between crystal structure and optical anisotropy of a thin film has been clarified. Therefore, it is possible by the methods of the first through the third prior arts to quantitatively evaluate the crystal orientation equal to a particle orientation. However, there is a problem in each of the methods that dimensions to be measured at a one time becomes narrow or it takes more time for measuring.
On the other hand, there is known a method for evaluating the anisotropy of a film by projecting a P polarized light into a thin film sample at an angle of polarization of a substrate, and measuring an intensity of S polarization component of a reflected light (see JP-A 2000-121496). With this method, it becomes possible to make the intensity of P polarization component in the reflected light minimum by projecting the P polarized light at an angle of polarization. So that, there is increased accuracy of measuring the intensity of the light having S polarization component which is generated by the anisotropy of the film. In a case where the anisotropic film is directly formed on the substrate, it is possible to make the P polarization component in the reflected light minimum by projecting the P polarized light at an angle of polarization on the substrate. Generally, however, when a sample having a multifilm structure such as the liquid crystal display component is used, it can not be possible to define with accuracy the angle of polarization which lacks of P polarization component of the reflected light so that it becomes difficult to apply this method.
Furthermore, S polarization component is included in the reflected light generated in response to the incidence of the P polarization. The S polarization component has an amount which depends on a degree of the optical anisotropy and a thickness of the area having the optical anisotropy of the sample. Particularly, the amount becomes small as the anisotropy is smaller or the thickness becomes thinner. As a result, limitation of detecting the optical anisotropy is determined by the intensity of the light source and sensitivity of a detector. Therefore, it is difficult to improve the detecting sensitivity.
The fourth prior art discloses a method of evaluating liquid crystal orientation of the oriented film by using an amount of the reflected light on a surface of the oriented film when the linear polarization is projected on the surface of the oriented film. However, the intensity of the reflected light generated in response to the incidence of the linear polarization having an arbitrary vibrating direction depends on not only the refractive index of the film but the thickness of the film. Therefore, in the fourth prior art, it is difficult to detect the anisotropy of the refractive index from the intensity of the reflected light.
Additionally, as disclosed in the fifth prior art, when the linear polarization is projected on the surface of the sample in perpendicular, the incident light and the reflected light pass through the same optical path. However, it is impossible to arrange the light source and the photo-intensity detector on the same optical path, and it is also impossible to carry out the perpendicular incidence.
When a beam splitter is used, it is unnecessary to arrange the light source and the photo-intensity detector on the same optical path. However, this beam splitter is not for maintaining the polarized state of the reflected light and a transparent light, so that it becomes impossible to carry out the perpendicular incidence.
In the fifth prior art, the light is projected into the surface of the film not in perpendicular but at an inclined angle. In this case, the incident light and the reflected light have two components. One of the components is S polarization component as a vibration component parallel to the sample surface. Another of the components is P polarization component as a vibration component perpendicular to both of the through direction of the light and the S polarization component. When the sample has same optical direction, the P polarization component and the S polarization component have different refractive indexes each other. When the light is projected into the sample surface at a predetermined angle, the polarized state of the incident light is specified as S polarization.
It is to be noted the P polarization component does not have the vibration direction parallel to or perpendicular to the film surface. In order to project the light of vibration direction parallel to a rubbing direction, namely, the direction of the orientation treatment, it is necessary to project the S polarized light into the sample in a direction perpendicular to the rubbing direction. On the other hand, in order to project the light of the vibration direction perpendicular to the rubbing direction, it is necessary to project the S polarized light in the direction in parallel with the rubbing direction.
In particular, in the case of using the liquid crystal oriented film which is subjected with the orientation treatment by rubbing the film surface with a cloth, a grooved anisotropic irregularity is produced on the film surface almost in parallel with the rubbing direction. Since the intensity of the reflected light becomes different according to the incident direction because of its anisotropic surface state, it is impossible to measure in accurate the optical anisotropy of the film by the method disclosed in the fifth prior art. Furthermore, when a sample of which orientation direction is unknown is used, the light is not projected so that S polarization direction becomes parallel to or perpendicular to the orientation direction.
As mentioned above, according to the fifth prior art, it is impossible to measure in accurate the anisotropy of the film on the basis of the result of measuring the intensity of the reflected light generated when the linear polarization is projected in the sample surface.
It is therefore an object of the present invention to provide a method of evaluating an anisotropic thin film, which is capable of evaluating an inplane distribution of an optical anisotropy of the thin film material in high speed and accurate.
It is another object of the present invention to provide an evaluating apparatus, which is capable of evaluating the inplane distribution of the optical anisotropy of the think film material in high speed and accurate.
Other objects of the present invention will become clear as the description proceeds.
According to the present invention, there is provided a method for evaluating an anisotropic thin film. The method comprises the steps of using a lens, a polarizer, and a phase converter to generate a light beam having a predetermined diameter and polarization state and to project the light beam as incident light into a thin film sample corresponding to the anisotropic thin film, detecting, by a two-dimensional photo-intensity detector through an analyzer, reflected light obtained from the thin film sample to produce a light intensity distribution, and evaluating an inplane distribution of an optical anisotropy of the thin film sample on the basis of the light intensity distribution.
According to the present invention, there is provided an evaluating apparatus for evaluating an anisotropic thin film. The evaluating apparatus comprising an optical system comprising lens, a polarizer, and a phase converter, the optical system generating a light beam having a predetermined diameter and polaraization state to project the light beam as incident light into a thin film sample corresponding to the anisotropic thin film, an analyzer disposed at an optically down stream side of the thin film sample, a two-dimensional photo-intensity detector disposed at an optically down stream side of the analyzer for detecting reflected light, obtained from the thin film sample, through the analyzer to produce a light intensity distribution, and an evaluating unit connected to the two-dimensional photo-intensity detector for evaluating an inplane distribution of an optical anisotropy of the thin film sample on the basis of the light intensity distribution.
When Rpp (p polarization component of the reflected light generated by projecting the P polarization), Rsp (s polarization component of the reflected light generated by projecting the P polarization), Rps (p polarization component of the reflected light generated by projecting the S polarization) and Rss (S polarization component of the reflected light generated by projecting the S polarization) are given for complex vibration index regarding the p component and S component of the reflected light which is generated by projecting p polarization or S polarization into the anisotropic thin film, Rsp and Rps have values if the sample in optically anisotropic, and have zero if the sample is optically isotropic.
Generally, absolute values of Rsp and Rps are very small for absolute values of Rpp and Rss. As the optical anisotropy of the sample becomes small, the absolute values of Rsp and Rps become small. In the method of measuring the anisotropy by combining only a polarizer and a detector, detected intensity is in proportion to squire of the absolute value of Rsp. Therefore, the detected intensity is quickly weakened when the optical anisotropy of the film becomes small.
On the other hand, in the optical system by combining the polarizer, a phase converter, and the analyzer of the present invention, it is possible to make the intensity of the light zero, which permeates the lowest detector against arbitrary combination of Rss, Rps, Rsp and Rpp. Namely, it is possible to change the reflected light from the film of the arbitrary optical character to the linear polarization in an upper stream. This kind of the linear polarization is generally given as:
axc3x97Rss+bxc3x97Rps+cxc3x97Rsp+dxc3x97Rppxe2x80x83xe2x80x83(1)
where a, b, c, and d are arbitrary complex numbers.
When the sample is isotropic, the linear polarization is given as:
axc3x97Rss+dxc3x97Rpp.xe2x80x83xe2x80x83(2)
When the direction of the analyzer is arranged so as to be an extinction state for the light of (axc3x97Rss+dxc3x97Rss), the detected intensity of the light from the anisotropic sample which is given by (axc3x97Rss+bxc3x97Rps+cxc3x97Rsp+dxc3x97Rss) is leaded as:
(a*xc3x97Rss*+d*xc3x97Rpp*)xc3x97(bxc3x97Rps+cxc3x97Rsp)+(axc3x97Rss+dxc3x97Rpp)xc3x97(b*xc3x97Rps*+c*xc3x97Rsp*)xe2x80x83xe2x80x83(3)
where a*, Rss*, D*, Rpp*, b*, Rps*, c*, Rsp* are conjugation complexes of a, Rss, d, Rpp, b, Rps, c, Rsp, respectively. As shown in Equation (3), primary term is included for the small amount of Rsp and Rps, and the conjugation complex thereof. The arrangement comprising the polarizer, the phase converter and the analyzer includes the terms proportional to small amount of primary Rsp and Rps of which the detected intensity has high-level relation with the anisotropy of the sample. Therefore, this method is higher in sensitivity for the anisotropy than the method of evaluating the anisotropy by combining the polarizer and the analyzer of the detected intensity of the small amount of secondary Rsp and Rps.
As mentioned above, in the present invention, the intensity detected by the arrangement of the combination with the polarizer, the phase converter and the analyzer includes the component proportional to the complex vibration refractive index of the p polarization and the s polarization component which are generated by projecting p polarization caused by the anisotropy of the film and s polarization p polarization, respectively. Therefore, the polarized state of the reflected light which is generated by projecting the light of the constant polarized state into the thin film sample of the optical anisotropy is changed in accordance with the incident direction of the light to the sample because of the optical anisotropy of the film. It is possible to select an appropriate incident direction in order to measure the inplane distribution of the optical anisotropy of the film by using the sample state having inplane rotating mechanism. Furthermore, it becomes possible to measure the inplane distribution of the optical anisotropy at an wide area by using the stage having the parallel moving mechanism.